Since when did kidnapping come to include adults too?

As per this link, the word 'kidnap' originated to denote nabbing away of a child. When and how did kidnap come to denote nabbing of adults?

Update: Just found a link to a 1650 book that mentions kidnapping of souls. Now not sure how correct the above link is.

Kidnap appears to be a back-formation from kidnapper (1682). This chart shows the relative use of “man was kidnapped”, “woman was kidnapped”, and “child was kidnapped”; there is a mysterious spike around 1850–1870 that may explain the subsequent increase in popularity of applying kidnap to adults, but I’m loath to draw any conclusions.

My guess is that kidnap became the general English word for abduction because we just didn’t have another word for it. Abduction didn’t refer to kidnapping till the 1760s, and the verb abduct is from as late as 1834. It makes sense that kidnap would have been extended to close the lexical gap.

The earliest OED citation of 1682 reads

Mr. John Wilmore haveing kidnapped a boy of 13 years of age to Jamaica

The next citation, dated 1688, is

John Dykes Convicted of Kidnapping, or Enticing away, His Majesty's Subjects, to go Servants into the Foreign Plantations.

Assuming subjects refers to more than children, we might reasonably, if not definitively, conclude that the change came about between the two dates.

The Online Etymology Dictionary defines "kidnap"as 1680s, compound of kid "child" and nap "snatch Away," variant of nab... In the book cited, The Old Whig, printed earlier in 1650, Samuel Chandler places the word kidnap in a spiritual context. He castigates the clergy of the day, whom he claims to be "shepherds and so have a right to fold their sheep that the wolves mayn't come near them and devour them." ..."They are to watch over the souls of the Christian people that thieves and robbers may not filch and kidnap them to destruction." p39

The argument here is metaphorical and linked to a number of Bible passages. The kidnapping relates to thinking adults of immature understanding, not to young children.

Kidnap is likely from "kid", a young goat (Hebrew gediy, a young goat, Strongs Concordance,1423) and nap a variant of nab, which Websters (1854) suggests is from KNAB, and means "to seize with the teeth," thus presenting us with a vivid word picture of the seizing of a young member (spiritually) of the flock (a young goat) by the teeth of wolves,(the clergy speaking hypocritically).

"They declare their assent to 39 whole articles only in jest and for financial gain." p398